A few years ago, AM Homes, still probably best known for her upmarket paedophile shocker The End of Alice, took an unexpected swerve into feel-good territory. Up until 2006, she was mainly a purveyor of suburban gothic: she adopted John Cheever's Westchester as her fictional terrain, but where the great short story writer gave the wealthy New York suburb an undercurrent of dread and misery, Homes turned it into a horror film. The End of Alice – pretentious, humourless, and horribly overwritten in a cod-Nabokov style – is actually far from her best in this vein; the short stories and Music for Torching, her 2003 novel about yuppie parents run amok, are a much better bet. In this period, Homes was often compared to Bret Easton Ellis – cynical and sensationalistic, certainly, but also clearly very talented.

Then, surprisingly, came her last novel, This Book Will Save Your Life, an LA-set story about a rich, isolated man who suffers a physical crisis and goes on a wild compassion spree: he buys a homeless man doughnuts; he takes in an unhappy housewife and a stray dog; he rescues a woman from the boot of a kidnapper's car. It had the same sense of spiritual emptiness as the earlier books (none too subtly, a sinkhole opens up in the hero's garden) but moved decisively in the direction of redemption. The book received a bumpy critical reception, but became a kind of cult success. Both reactions were understandable: it was kitschy and bordered on the inane, but there was something appealing about its mixture of the apocalyptic and the perkily upbeat, caught nicely by John Waters when he said: "If Oprah went insane, this might be her favourite book."

Homes's new novel starts in the style of Music for Torching, then veers off in the direction of This Book Will Save Your Life. The first section is a tour-de-force of pitch-black comedy set, again, in Westchester. The story begins at Thanksgiving: Harry Silver, an under-achieving Nixon scholar, describes his hatred for his taller, richer, more aggressive brother George, a TV network boss, who sits "at the head of the big table, picking turkey out of his teeth, talking about himself". George's children, aged 10 and 11, are "sat like lumps at the table, hunched, or more like curled, as if poured into their chairs, truly spineless, eyes focused on their small screens, the only thing in motion their thumbs – one texting friends no one had ever seen and the other killing digitised terrorists". Harry is picking the stuffing out of the "heirloom" turkey carcass in the kitchen, his lips smeared with grease, when his sister-in-law Jane suddenly kisses him on the lips.

A few months later George is arrested. He has run a red light and smashed into a people carrier, killing a couple and leaving their son orphaned; it's not clear that it was an accident. Then, in startlingly quick succession, all sorts of bad things happen: an affair, a murder, a divorce; and Harry suddenly finds himself in sole charge of his niece and nephew. After the first exhilarating 50 pages, the reader wonders: where on earth can Homes go now?

The answer seems to be: everywhere. The rest of the book is a digital-age picaresque, a series of bizarre, episodic adventures. People are hospitalised, repeatedly; sacked, kidnapped, and incarcerated in sinister experimental correctional facilities. There is child abuse, abuse of prescription drugs, internet sex, and a swingers' party at a Laser Tag Emporium. There are subplots to do with a murdered woman, a Bar Mitzvah in a South African village, and the discovery that Richard Nixon wrote dark short stories. The overall direction of travel, though, is towards the light. The children, says Harry, push him into being "a better version of myself", and an alternative family unit forms under his supervision. Dark satire gives way to spiritual uplift.

At the fulcrum between the dark and light is a vision of an atomised, alienated society elaborated in what is clearly the novel's keynote speech: "There is a world out there, so new, so random and dissociated that it puts us all in danger. We talk online, we 'friend' each other when we don't know who we are really talking to – we fuck strangers. We mistake almost anything for a relationship, a community of sorts, and yet, when we are with our families, in our communities, we are clueless, we short-circuit and immediately dive back into the digitised version …" The "loss of the human touch" in everyday life is a recurring theme; towards the end, Harry is told: "You're human now."

This movement from irony to sincerity is a very characteristic one in young-ish American writers. You also see it in The Simpsons, and in indie films such as Little Miss Sunshine, where satire gives way to a warm alternative community. It's difficult to do well: darkness and despair often present themselves in more aesthetically pleasing forms than kindness and optimism. And May We Be Forgiven is a very uneven novel, rickety, meandering and repetitive. There are far too many forgettable sub-plots and similar comic routines. Its recipe for redemption, as in This Book Will Save Your Life, involves an uneasy mixture of truism (be nice to children, animals, strangers) and kitsch (form friendships with immigrants who work at fast food outlets, listen to the wise medicine man). It is, however, often very funny, in a bad-taste way. Homes's dialogue drives a lot of the action – and she's very good at dehumanising sales patter, and smart, classic Hollywood-style rat-a-tat-tat exchanges. Some of the half-ironic, half-sincere set-pieces, such as Harry's visit to his nephew's ridiculously well-appointed private school, are excellent. And the novel is consistently interesting in more sombre ways, too, as when Harry discusses the "rusty sense of disgust" that he suspects might be his soul. May We Be Forgiven is a semi-serious, semi-effective, semi-brilliant novel which could not be called, overall, an artistic success. But you'd have to have no sense of the absurd, and no sense of humour, not to be pretty impressed.